1. Field of the Invention
The present invention is related to the measurement of liquid in a tank that is subject to tilting, and, more particularly, is related to the measurement of the weight of the liquid in the tank by determining differences in pressures at multiple locations in the tank.
2. Description of the Related Art
The measurement of the fuel remaining in the fuel tanks of an aircraft is highly important in order to assure that an aircraft is not flown beyond the limits of the available fuel. Fuel measurement techniques have evolved from the original method of inserting a rod into the tank prior to a flight. A current industry standard for measuring fuel uses capacitive probes, which measure the height of the fuel in a tank by measuring the change in capacitance of concentric tubes. The principle behind this approach is that changing fuel levels change the dielectric constant between the concentric tubes. In particular, a higher fuel level causes a greater capacitance, and a lower fuel causes a lower capacitance. The value of the capacitance of the concentric tubes is very small (e.g., on the order of 50 to 100 picofarads). Therefore, an accurate measurement of such a small capacitance is challenging, especially, since the stray wiring capacitance can far exceed 100 picofarads. Thus, capacitive fuel probes are very expensive and may cost in a range of $600-$2,000 per probe. Furthermore, multiple probes may be required in each tank. Since the capacitive probes are operated electronically, a portion of the electronics are typically located in the fuel tanks, which may present a risk of explosion. Accordingly, a need exists for simpler, safer and less expensive fuel probes, which provide accurate measurements of fuel during aircraft flight.